In general terms, the main research conducted in this proposal is directed toward a better understanding of the action of narcotic analgesics and the development of tolerance and physical dependence to these drugs. More specifically, the proposal concerns the following aspects: 1) Characterization of central narcotic receptors; 2) Naloxone-releasable opiate binding sites in superfused brain slices; 3) Physiological role of endogenous opioid peptides; 4) Relation of biogenic amines to the expression of morphine abstinence; 5) Factors involved in the enhancement of narcotic antagonistic potency; 6) Compounds which accelerate the development of tolerance; 7) Morphine-d-amphetamine interaction.